The invention relates to the general field of sensors, such as for example temperature, pressure, displacement sensors, etc.
More particularly, it relates to the compensation of measurement errors related to the output impedance of a sensor.
The invention has a preferential but non-limiting application in the aeronautical field, where many sensors are used (on-board an aircraft for example).
In practice, a sensor is generally connected to a digital computer which is responsible for receiving and processing measurement data transmitted from the sensor, the sensor and the digital computer thus being part of an acquisition chain.
Now, it is known that, when a sensor which may be assimilated to an equivalent voltage generator in series with the source impedance is connected to a digital computer having finite input impedance, a measurement error occurs if the ratio between the output impedance of the sensor and the input impedance of the computer is not negligible. This undesirable error occurs systematically and directly depends on the type of sensor and on the relevant computer.
In reality, even when the type of sensor is set for a given application, significant variations of the equivalent series impedance of the sensor often appear from one part to the other (production variations). In this case, it is usually possible to at best compensate for half the error due to the variation of the equivalent series impedance of the sensor.
Further, for certain types of sensors (potentiometers for example), a variation of impedance may even occur depending on the measured point of this equivalent series impedance. In this case, the equivalent series impedance variation resulting from the measurement point generates an error which varies non-linearly depending on the measurement point. This non-linear error may theoretically be compensated but the required compensation strongly complicates the algorithm for converting the measurement into a physical quantity at the digital computer, which most often leads to the use of approximation functions which simplify this algorithm at the expense of the attained accuracy.
For certain sensors, the error induced by these differences in impedance may be significant, reaching through to the maximum total error which is tolerated for the relevant acquisition chain (set to 1% for example). This impedance error will thus be added to the other inaccuracies which generally affect an acquisition chain.
Therefore there exists a need for compensating in a simple, rapid and efficient way for the measurement error affecting a sensor connected to a digital computer, and more particularly when this computer has non-negligible equivalent series impedance against the input impedance of the computer (also called “conditioner”).
Further, a same computer may be designed for processing different types of sensor, each sensor having its own output impedance, which is unknown. Therefore it is not possible to apply error compensation a priori since the error will vary according to the sensor used.